Just went through the stock tires which came with my new 2014 500 EXC and needing some recommendations for new wheels. I ride mostly desert single track (sand and rock) and some pavement to get me there. Very willing to spend up to nail down a great tire.

I have a 2014 500EXC and I would not recommend a set of Dunlop D606's. Rear is wearing extremely fast for 10% road 90% desert riding, although not as fast as the stock Maxxis rear, and the front is super unpredictable in the dirt. Nothing like turning to avoid a bush at speed and having the front end step away from you to suddenly find traction out of nowhere. Had to stop and check myself afterwards on a couple of occasions.
I prefer running an MT43 trials rear for the majority of riding I do, other than desert. The D606 rear is decent and better than the trials tire in the desert but faster wearing than the trials tire for sure. Whatever you do, I suggest finding the most aggressive front knobby you can.